In many instances, it is highly important that homeowners and operators of commercial establishments be promptly made aware of the occurrence of a power failure since considerable damage or property loss may occur if the power failure continues for extended lengths of time. If the proprietor or homeowner is alerted, emergency power generating equipment could be pressed into service or other steps taken to reduce the incidence of damage or loss of perishables.
These circumstances, for example, include the shutdown of refrigerators, freezers, and/or the interruption of service of sump pumps. If the power failure occurs at night, the homeowner may remain unaware of the power failure until a considerable lapse of time has transpired and the damage or loss already occurred.
At the same time, many instances of interruption of service are relatively short in duration such that damage or loss would not occur and, accordingly, an alarm system for monitoring such failures would desirably not sound until after the failure has persisted for some time after which preventive steps should be taken.
U.S. Pat. Nos. 4,001,803 and 3,958,212 both disclose typical prior art power failure alarms. These arrangements disclose a coil used to hold an alarm device in the inoperative position, which hold-in device is powered by the circuit to be monitored, thus upon interruption of the power, the alarm is sounded.
However, this results in the sounding of the alarm for even momentary power interruptions such as to create unnecessary disturbances and the necessity to reset the device. Particularly, this is so since these interruptions could occur at relatively inconvenient times such as during the nighttime.
An additional disadvantage of this approach is the necessity for an auxiliary power source, i.e., batteries, to power the alarm. Batteries degenerate with time and it is possible that the relatively long intervals of time during which the device would not get attention could very well lead to the failure of the device when needed.
U.S. Pat. Nos. 3,588,856 and 1,999,811 disclose alarm arrangements for circuitry which incorporates delays. These appear to allow for a slight delay before the activation of the alarm device is produced and do not appear to interpose delays of sufficient duration to be applicable to the situation described above. In addition, these arrangements are relatively complex and not well suited to use by the homeowner.
Accordingly, it is an object of the present invention to provide a power failure monitor or alarm which provides an alarm indication in the event of a power failure in the circuit to be monitored, but only after a predetermined adjustable delay of sufficient duration to eliminate giving false alarm conditions. That is, only upon continuance of the power failure or interruption for an interval of sufficient length is the alarm given such that steps may be taken to protect property endangered by the power failure.
It is another object of the present invention to provide such a power failure monitor which does not depend on auxiliary power sources such as batteries, but which is self-contained so as to be relatively reliable in operation.
It is yet another object of the present invention to provide such a power failure alarm which is simple and reliable in operation and which may be manufactured at relatively low cost.